Compose onValueChange behaviour isn't consistent - kotlin

Question

I'm making a sudoku game and solver. For my user interface I used LazyVerticalGrid to create a 9x9 grid. I successfully made it so when you click on a cell it will only accept digits [1-9] via an OutLinedTextField. I then added a conditional that only empty cells would have the text field applied. That worked and only those cells could be altered but when I do that the logic that only accepts digits doesn't work and the program crashes. If I comment out the conditional statement and the OutLinedTextField is applied to all cells it works again. I get the following error.
Also if I add conditionals for backgroundColor or Content Color the same thing happens and the program crashes if a non digit is pressed. I'm not sure why the conditionals affect the onValueChange logic. Why is this and how do I fix it?
fun displayPuzzle(answer: Array<Array<IntArray>>) {
var list: SnapshotStateList<String> = mutableStateListOf()
for (x in answer[0]) list.addAll(x.map { it.toString() })
var columnHeighty by remember { mutableStateOf(0F) }
var columnWidthx by remember { mutableStateOf(0f) }
var pad = 20.dp
LazyVerticalGrid(
columns = GridCells.Fixed(9),
contentPadding = PaddingValues(
start = pad,
top = pad,
end = pad,
bottom = pad
)
) {
items(list.size) { index ->
Card(
shape = RectangleShape,
backgroundColor = Color.Red,
modifier = Modifier
.requiredWidth(83.dp)
.fillMaxWidth()
.fillMaxHeight()
.onGloballyPositioned { coordinates ->
columnWidthx = coordinates.size.width.toFloat()
columnHeighty = coordinates.size.height.toFloat()
},
//backgroundColor = if (list[index].toInt() == 0) Color.Yellow else Color.White ,
//contentColor = if (list[index].toInt() == 0) Color.Blue else Color.Black ,
border = BorderStroke(width = 1.dp, color = Color.Black)
) {
Text(
text = list[index],
fontWeight = FontWeight.Bold,
fontSize = 30.sp,
color = Color(0xFF000000),
textAlign = TextAlign.Center,
modifier = Modifier
.padding(23.dp)
.clickable { }
)
}
// When the if statement is included the program crashes on a non digit entry
//if (list[index].toInt() == 0) {
val pattern = remember { Regex("[1-9]") }
var value by remember { mutableStateOf("") }
OutlinedTextField(
keyboardOptions = KeyboardOptions(keyboardType = KeyboardType.Number),
colors = TextFieldDefaults.outlinedTextFieldColors(cursorColor = Color.Transparent),
textStyle = TextStyle(color = Color.Red),
modifier = Modifier
.fillMaxHeight()
.padding(vertical = 10.dp, horizontal = 10.dp),
value = value,
onValueChange = { if (it.isEmpty() || (it.matches(pattern) && (it.length == 1)))
value = it
list[index] = value}
)
//}
}
}

Answer 1

Your game crashed because you trying to convert for example 'a' to Int value and runtime throws NumberFormatException.
You need to use:
if (list[index].toIntOrNull() == null)
This condition will be triggered if a non-decimical number is obtained from your SnapshotStateList
Explanation: toIntOrNull() returns Int from String (example: "4".toIntOrNull() - returns 4) otherwise it returns null